What is the mass of oxygen atoms in 0.200 mol of calcium nitrate, Ca(NO3)2? (Molar masses: Ca = 40.1 g/mol, N = 14.0 g/mol, O = 16.0 g/mol)
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Correct answer
A. 19.2 g
Principle or equation
Each formula unit of Ca(NO3)2 contains 6 oxygen atoms. Mass of oxygen = moles of compound × 6 × molar mass of O.
Why this answer is correct
Moles of O = 0.200 × 6 = 1.20 mol. Mass of O = 1.20 × 16.0 = 19.2 g.
Example
For 0.100 mol Ca(NO3)2: O moles = 0.600, mass = 9.60 g.
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